title: The etiology of refractive changes at high altitude after radial keratotomy. Hypoxia versus hypobaria.
abstract: OBJECTIVE
  Refractive changes at high altitude that occur after radial keratotomy (RK) may be caused by hypoxia or hypobaria.
  
  
  METHODS
  A prospective study was performed to evaluate the effects of hypoxia on RK and non-RK corneas.
  
  
  METHODS
  There were 20 RK and 20 control eyes.
  
  
  METHODS
  These eyes were subjected to ocular surface hypoxia using an air-tight goggle system at sea level for 2 hours.
  
  
  METHODS
  Keratometry, cycloplegic refraction, and pachymetry were evaluated using repeated measures analysis of variance.
  
  
  RESULTS
  A significant hyperopic shift (P < 0.0001) and corneal flattening (P < 0.0013) occurred in all subjects with RK compared with those of control subjects. Corneal thickening occurred symmetrically in both groups.
  
  
  CONCLUSIONS
  These results suggest that refractive changes in subjects with RK occur at high altitude as a direct result of corneal hypoxia.
authors.affiliation: Ophthalmology Service, Madigan Army Medical Center, Tacoma, Washington 98431-5000, USA.
authors.forename: R K
authors.initials: RK
authors.lastname: Winkle
authors.forename: T H
authors.initials: TH
authors.lastname: Mader
authors.forename: V C
authors.initials: VC
authors.lastname: Parmley
authors.forename: L J
authors.initials: LJ
authors.lastname: White
authors.forename: K A
authors.initials: KA
authors.lastname: Polse
mesh_terms: D000328:Adult; D000531:Altitude; D001274:Atmospheric Pressure; D003315:Cornea / Q000601:surgery; D005260:Female; D006801:Humans; D006956:Hyperopia / Q000209:etiology*; D000860:Hypoxia / Q000150:complications*; D007646:Keratotomy, Radial; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000601:surgery; D011183:Postoperative Complications; D011446:Prospective Studies